Ceramic substrates are of particular importance in the microelectronics industry for the mounting, packaging and cooling of integrated devices. The fabrication of ceramic substrates is well known and is described, for example, in U.S. Pat. No. 5,130,067 issued to Philip L. Flaitz et al. on Jul. 14, 1992 and assigned to the present assignee. Burn-out and sintering comprise the final steps in the fabrication sequence. Burn-out drives off the volatile binder utilized in the ceramic slurry into a vented atmosphere. It is well known to be beneficial to apply weight to the ceramic substrate during sintering to minimize distortion due to shrinkage and cambering of the substrate.
Provision has been made in the prior art cited in the Flaitz et al patent, namely, U.S. Pat. No. 4,340,436 issued to Dubetsky et al on Jul. 20, 1982 and assigned to the present assignee, to accomplish burn out and sintering in a two step process. In the first step, the substrates are loaded into a furnace held at a temperature range and for a time sufficient to drive off the binder, cooled to room temperature, and then unloaded. The same substrates are placed into a configuration to maintain substrate flatness and then reloaded into a furnace and exposed to a higher temperature range and a longer time than were employed in the previous burn out cycle.
U.S. Pat. No. 5,130,067, cited above, teaches a process of applying an external load during sintering of a green ceramic substrate to constrain the substrate in the and Y directions and thereby control dimensional stability. The load is applied by weights that are either in place at the start of the heating cycle or remotely applied to the substrate by pneumatic, hydraulic or mechanical levers.
U.S. Pat. No. 4,259,061 issued to Derry J. Dubetsky on Mar. 31, 1981 and assigned to the present assignee describes the use of ceramic coated refractory plates used for setters onto which alumina substrates are placed to control shrinkage uniformly.
U.S. Pat. No. 5,364,608 issued to James P. Edler on Nov. 15, 1994 discloses a method to form sintered silicon nitride articles within a walled container which is vented to the furnace in which it is placed.
U.S. Pat. No. 5,376,601 issued to Yoshihiro Okawa on Dec. 27, 1994 cites the components used in the sintering of AlN components that resist deformation at high temperatures. When the sintered AlN product itself is used as setters and supports for a baking jig to hold other AlN products to be sintered, the patent states that the setters and supports of the jig are not deformed under the baking conditions and, hence, do not cause the molded articles to be deformed.
The following Japanese Patent Publications show the use of refractory boxes for sintering aluminum nitride substrates placed therein.
______________________________________ Publication No. Publication Date Inventor ______________________________________ 02-302088 December 14, 1990 Omote Koji et al. 03-097682 April 23, 1991 U. Etsuro et al. 04-198062 July 17, 1992 H. Michio et al. 05-009076 January 19, 1993 T. Yutaka et al. 05-105526 April 27, 1993 Akiyama Susumu ______________________________________
This invention overcomes the above-mentioned problems and short-comings of the prior art, and provides a refractory box that remains open during a first temperature range, such as, during binder burn out, and automatically in-situ seals itself during a second temperature range, such as during the sintering cycle. It further provides a method to apply a weight onto a substrate at a predetermined temperature within the box.